The invention relates to the field of flexographic printing machines and the object of the invention is the device called doctor blade chamber for the inking of an anilox roll.
The printing groups of the flexographic printing machines comprise a roller called anilox roll furnished for the inking of a plate supported by another roll called plate holder. The inking of the plate is performed by a transfer of the ink from the anilox roll to the holder plate.
A problem to resolve comprises the inking of the anilox roll. In the running fashion the anilox roll furnishes a cellular outer surface for the receipt of the ink.
One knows a first mode of inking an anilox roll, comparatively old, which consists in having the anilox roll dabble in a bath of ink. At least one intermediate roll is interposed between the anilox roll and the plate holder in order to obtain a suitable and proper distribution of the ink over the complete surface of the plate. A major inconvenience of this mode of inking comprises its complexity and the splashes of ink which result from the dampening and which are making it necessary to protect the space surrounding the anilox roll by a careenage.
In order to relieve this inconvenience devices called doctor blade chambers have been proposed for the inking of the anilox rolls. These devices comprise a sealed box permanently filled with ink and disposed on the side of the anilox roll in such a way to envelope a portion of the rotating surface of the anilox roll. A circulation of the ink in the interior of the box maintains the homogeneity of the ink. According to various variations, the ink is drained out of the box be it by using directly the rotary motion of the anilox roll or be it by associating here different reflux means. The sealing between the box and the anilox roll is obtained on the one hand at the ends of the anilox roll by a pair of cheeks furnished with sealing members and on the other hand along the anilox roll by at couple of scraper blades disposed respectively upstream (positive scraper blade) and downstream (negative scraper blade) of the inking zone of the anilox roll, wherein the negative scraper blade is in addition destined to smoothe ink on the surface of the anilox roll.
A first inconvenience of this type of device is based on a random inking of the exterior surface of the anilox roll and on an irregular distribution of the ink on the anilox roll caused by the prevailing pressure in the box which does not favor a proper and suitable filling of the cells.
A second inconvenience flows from the circulation of the ink under pressure in the interior of the box, which imposes important limitations with respect to the sealing between the box and the anilox roll, in particular at the ends of the latter anilox roll, and the frequent replacement of the sealing members requires a detrimental stop in the operation of the machine.
It is an object of the invention to furnish a device of the kind of said doctor blade chamber for the inking of an anilox roll of a flexographic printing machine, which guarantees a homogeneous inking of the anilox roll and the structure of which renders the maintenance of the device quick and easy.
The inventive path has comprised starting with the statement referred to above and in meeting the customs taken in the field, to propose a doctor blade chamber wherein the ink circles naturally by gravity in the interior of the doctor blade chamber, from a supply chamber wherein the ink is brought out to a discharge chamber, and wherein the ink flows out of said discharge chamber. A retaining blade is interposed between the two said chambers and the overhang of the discharge chamber in order to furnish an obstacle to the natural circulation of the ink and to manage a retention of the ink, which ink is preferably naturally conducted from the reserve up to upstream of the negative blade under the effect of the rotation of the anilox roll. Circulation channels of the ink allow an escape of the ink outside of the reserve toward the discharge chamber in order to maintain the natural circulation of the ink between the two chambers even though the retaining reserve blade is present.
These arrangements are such that in the first place the circulation of the ink in the interior of the doctor blade chamber is not forced and is effected at atmospheric pressure and in the second place that the cushion pad of ink formed upstream of the negative blade does not cause any unsuitable thrust pressure on the ink of the kind present in the prior art wherein the ink circulates without pressure in the interior of the box. There results a homogeneous inking and a uniform and constant smoothing of the anilox roll and finally a suitable and proper distribution of the ink on the entirety of the periphery of the anilox roll.
It is observed that the selection of a blade as a hindrance member to the natural flow of the ink in the interior of the box is preferred based on the fact that the said blade is not only suitable to manage the retaining of the ink, but also, and then called distributor, is suitable to furnish a proper and suitable distribution of the ink on the anilox roll and wherein an equivalent member, which performs only the function of a hindrance to the natural flow of the ink, can be substituted for said blade for departing so much from the general rule of the invention, however in this case a distribution member of the ink on the anilox roll has to be associated with the blade.
In other words, one understands that the retaining blade is intended not only to manage the retaining of the ink upstream of the negative blade but also, called also distributor, to distribute and to smoothe the ink on the anilox roll.
The applicants propose according to the inventive concept to close the end faces of the box of the doctor blade chamber by means of cheeks or side plates, in particular made of nylon, and held in simple contact against the end faces of the anilox roll, wherein the said cheeks or side plates form not only the end wall of the box but also form by themselves sealing members between the box and the anilox roll; it is noted that the seal is obtained in this fashion thanks to the circulation by simple gravity of the ink in the interior of the box.
Finally and according to an advantageous embodiment, the negative blade is joined to the box by the intermediary of a detachable support for offering an easy access to the interior of the doctor blade chamber, in particular with regard to the cleaning of the doctor blade chamber, and for the purpose of allowing a quick and easy replacement of the negative blade by a replacement of the support by another support previously furnished with the blade, without having to interrupt for a long time the functioning of the machine and without having to change the position of the doctor blade chamber relative to the anilox roll and therefore to have to empty this latter doctor blade chamber.